Ball bats and other sporting-good implements are often made from composite materials. Composite components are generally formed from at least one layer of a fibrous material, such as carbon or fiberglass, which is coated in a matrix material, such as a resin, and cured to form a hardened structural material. One known method of forming composite components involves stacking or laying up multiple layers that have been pre-impregnated with resin, and curing the assembly with heat (often called a “pre-preg” process). Another known method of forming composite components is resin-transfer molding (“RTM”). RTM methods typically include providing a layer of fibrous material in a mold, injecting a resin material into the mold to saturate the fiber material, and using heat to cure the resin-coated fiber into the hardened composite layer. Composite manufacturing methods require substantially uniform resin flow during the injection or curing process to ensure structural uniformity. They also often require dedicated tooling molds that can be expensive to modify or replace.
For most players, a ball bat generally has a better feel and higher performance when the barrel exhibits a relatively low compression. Lower compression may result in a composite bat, for example, from forming the bat with multiple concentric walls or layers. Such walls or layers are typically molded separately and assembled together after molding, or they can be laid up with layers of polymer or plastic sheeting to separate the composite layers. But these existing techniques often require significant tooling costs or production steps that can complicate the manufacturing process. For example, when using polymer sheets to separate layers in composite-laminate walls, resin generally flows along one side of the polymer sheet to a greater extent than the other side—rarely evenly distributing along both sides—resulting in an incomplete and undesirable distribution of resin.
Bats may also have improved feel when they include some form of damping to lessen vibrations resulting from impact with a ball. During a typical impact, a bat momentarily flattens or flexes at the site of impact, followed by repeated oval-shaped oscillations after the impact. Damping elements have typically been located at the barrel-handle connection, or at the knob end of a ball bat. A rubber connector positioned between a handle and a barrel, for example, can be used to absorb some of the energy resulting from post-impact oscillations. Damping may also contribute to lower batted-ball speeds to facilitate a bat's compliance with regulatory association standards.